In the prior art, the rolls in paper machines and paper finishing devices, with the exception of rolls in which the roll mantle can move in relation to the roll axle, have, as a rule, been journalled on the frame constructions of the machine by means of roller bearings. In particular, in the case of rolls that form a nip, such as calender rolls, soft calender rolls and size press rolls, such mounting by means of roller bearings has caused certain problems, whose solution has required particular arrangements. In nip rolls it is necessary to measure the nip load, but in some cases the measurement has been problematic. For example, in a soft calender it is necessary to run in a range of linear load in which the bearing load is close to zero, which is highly problematic from the point of view of a roller bearing, because in a zero load situation the rolling members in the roller bearing are capable of gliding to a considerable extent in relation to the bearing races, in stead of rolling, which results in quite rapid damaging of the bearing. Also, for example, in size presses the running takes place with quite low linear loads so that low loads are applied to the rolls. In heatable rolls, such as, for example, calender rolls and equivalent, the problem is mainly related to successful lubrication of the bearing, and not so much to control of the bearing play. Also out of this reason, in the case of roller bearings, it has been necessary to employ special arrangements. Roller bearings also involve a problem in respect of the limitation of speed. Such limitations in respect of the speed of rotation involve, for example, the generation of heat in the bearing and, in this connection, the possibility of cooling the bearing. Among other things, out of this reason, roller bearings impose a certain limit on the speed of rotation, which limit the manufacturer of the bearing does not permit to be exceeded. As was already stated earlier, the accuracy of rotation of the bearing is limited, among other things, because of inaccuracies in the roller members and bearing races. Even if, in a conventional roll, all the components were manufactured as precisely as possible, the errors arising from inaccuracies are summed up in an assembled roll.
Owing to the problems related to the mounting of rolls by means of roller bearings, in recent years, various glide bearing solutions have been developed for journalling of rolls to an ever increasing extent. The construction and the embodiment of a glide bearing in themselves are quite simple, but, in particular in the case of nip rolls, the problems often arise from the way in which a glide bearing can be controlled in view of controlling the loads applied to the bearings and the radial shifting of the roll. Thus, the problems are mainly concentrated on the control systems of a glide bearing.
With respect to the prior art, reference is made, for example, to the EP Patent No. 158,051, which concerns journalling of a washing drum. In this solution, tie journalling has been accomplished as a mounting by means of glide bearings by means of hydrostatic bearing segments. A mode of journalling in accordance with said paper can, however, not be employed, for example, in calender rolls that are in nip contact, because the mode of journalling of said EP publication does not involve any possibility of radial movement in the bearing itself. Nor can the loading of the bearing be varied in any way, and separate spring elements are required in order to attenuate oscillations. With respect to the prior art, reference is made further to the FI Patent Application No. 942756, in which a bearing for a heated roll is described. Also this mode of journalling involves the drawback that there is no radial possibility of shifting, because at least one hydrostatic bearing segment in the glide bearing solution is fully stationary and fixed in the radial direction in relation to the frame construction, and, thus, a roll journalled by means of said bearing cannot be displaced, for example, in the direction of the nip plane.